This invention relates generally to load responsive fluid power and control systems, in which the flow out of the pump is automatically varied to maintain a constant pressure differential between the discharge pressure of the pump and the maximum system load pressure.
In more particular aspects this invention relates to load responsive fluid power and control systems, in which the flow of the pump is varied by a bypass control.
In still more particular aspects this invention relates to a load responsive fluid power and control system, in which the flow out of the system pump is varied by variation in the rotational speed of the prime mover driving the pump.
Load responsive fluid power and control systems are very desirable, since they provide an exact and accurate proportional control of system loads. Such systems may use an inexpensive fixed displacement system pump, usually driven at a constant speed and provided with a bypass type output flow control, as disclosed in U.S. Pat. No. 3,488,953, issued to Haussler. Although such a system provides high performance at low cost, it is comparatively inefficient especially with a duty cycle utilizing low system flows at high pressure. This drawback can be overcome by a system as disclosed in U.S. Pat. No. 3,444,689, issued to Budzich, in which the flow output of the pump is varied by change in the pump displacement, in response to a load pressure signal. Such a system is very efficient but, since it uses a variable displacement pump, it becomes relatively expensive.